1. Field of the Invention
The present invention relates to a color flat-panel display, and more particularly, to an electrode structure of a color flat-panel display.
2. Discussion of the Related Art
Recently, an electroluminescent display (ELD), a plasma display panel (PDP), a liquid crystal display (LCD) and the like have been developed as a color flat-panel display. In comparison with a cathode ray tube (CRT) that uses an electron beam, however, a conventional color flat-panel display has not reached a satisfactory level in view of performances such as a luminance, a contrast and a color reproduction.
To overcome shortcomings of the conventional color flat-panel display (the ELD, the PDP and the LCD) and implement a high-quality image comparable to the CRT, there have been proposed an improved color flat-panel display that is based on a screen scanning of an electron beam.
Meanwhile, Japan Laid-open Publications No. 3-184247 and No. 3-205751 disclose an image display apparatus for displaying a high-quality image comparable to the CRT on a flat-panel display that uses an electron beam, in which an image displayed on a screen is divided into unit cells constituting a matrix and then an electron beam is deflectively scanned to each unit cell, so that a phosphor screen is light-emitted to thereby display an entire color image.
FIG. 1 is a view of a conventional color flat-panel display based on a screen scanning of an electron beam.
FIG. 1 is an exploded perspective view showing main elements of the conventional color flat-panel display. Referring to FIG. 1, the conventional color flat-panel display includes a rear glass 1, a rear electrode 2, a filament cathode 3, a control electrode 4, a signal modulation electrode 5, a focus electrode 6, a horizontal deflection electrode 7, a vertical deflection electrode 8, and a front glass 9, all of which are arranged one after another. In addition, the rear glass 1 and the front glass 9 are sealed to maintain a vacuum state.
In more detail, the rear electrode 2 is formed of a conductive material such as metal and graphite on a flat panel. The rear electrode 2 is arranged in parallel with the filament cathode 3 and a negative voltage is applied to the rear electrode 2 to thereby cause an electron emitted from the filament cathode 3 to be directed toward the screen.
Generally, the filament cathode 3 is formed coating an oxide cathode material on a surface of a tungsten wire. At this time, a plurality of filament cathodes are arranged to generate the electron beam constantly distributed in a horizontal direction.
As an electrode for drawing the electron beam 11, the control electrode 4 is spaced apart from the filament cathode 3 by a predetermined distance and disposed in a direction of the screen. Also, the control electrode 4 is faced with the rear electrode 2 and formed of a conductive plate in which passing holes are disposed at each predetermined distance in a horizontal direction and formed on a horizontal line facing each filament cathode 3 by a predetermined distance.
The signal modulation electrode 5 includes a row of conductive plates, each of which is arranged on a position facing each passing hole of the control electrode 4 and spaced apart from the control electrode 4 by a predetermined distance. At this time, each conductive plate is thin and long in a vertical direction. Each conductive plate of the signal modulation electrode 5 has passing holes formed in the same plane on a position facing each passing hole of the control electrode 4.
The focus electrode 6 is formed of a conductive plate having passing holes formed on each position facing each passing hole of the signal modulation electrode 5. The horizontal deflection electrode 8 includes two conductive plates meshed with each other on a sectional portion and spaced apart by a predetermined distance on the same plane.
Further, the vertical deflection electrode 8 also includes two conductive plates meshed with each other on a sectional portion and spaced apart by a predetermined distance on the same plane.
Generally, all of the above-described electrodes are manufactured using an Invar (Fe—Ni alloy) in order to prevent an image quality from being degraded due to a thermal deformation. Each of the control electrode 4, the signal modulation electrode 5, the focus electrode 6, the horizontal deflection electrode 7 and the vertical deflection electrode 8 is joined with an insulating adhesive.
FIG. 2 is a view explaining a phosphor screen of the conventional color flat-panel display.
Referring to FIG. 2, a phosphor screen 15 is formed on the front glass 9 and R, G and B phosphors 12 are coated on an inner side of the front glass 9. Black matrixes (BM) 14 are formed between the phosphors 12.
In addition, a metal back 13 is formed on the phosphors 12 to thereby reflect and project a light generated by the phosphors 12 on the front glass 9.
On the basis of the above structure, an operation of the conventional color flat-panel display will be described below with reference to FIGS. 1 and 2.
If a voltage is applied to the filament cathode 3, electrons are emitted. At this time, the filament cathode 3 is heated by passing a current therethrough in order to easily obtain the electron emission.
The electrons emitted from the filament electrode 3 are divided into multiple parts by the passing holes of the control electrode 4 and its amount is controlled.
A passing amount of the electron beam 11 passed through the control electrode 4 is controlled corresponding to an image signal at the signal modulation electrode 5.
The electron beam 11 passed through the signal modulation electrode 5 is focused at the passing holes of the focus electrode 6 due to a static lens effect. The electron beam 11 is deflected by passing both the horizontal deflection electrode 7 and the vertical deflection electrode 8 and then it is scanned to the phosphor 12 of corresponding unit cell 10, thereby displaying a desired image.
At this time, a voltage applied to the electrode adjacent to the screen is maximally of 600 V and a voltage of the screen is approximately of 10,000-14,000 V.
In other words, since a high voltage of approximately 10,000 V is applied to the metal back 13, the electron beam 11 is accelerated to a high energy and collided against the metal back 13, thereby light-emitting the phosphor 12.
FIG. 3 is a view showing a structure of the vertical deflection electrode 8 in the conventional color flat-panel display.
As shown in FIG. 3, the vertical deflection electrode 8 is made in a structure that two conductive plates 8a and 8b are meshed with each other on a sectional portion and spaced apart by a predetermined distance on the same plane.
In other words, if positive and negative voltages are applied to the conductive plates 8a and 8b respectively, an electric field is generated, and the electric field causes the electric beam to be deflected, thereby achieving a vertical deflection.
In addition, a horizontal deflection is achieved in the horizontal deflection electrode 7 by the same principle as the vertical deflection.
FIG. 4 is a view explaining an assembly process of the electrodes, in which a pre-sintering state and a post-sintering state are shown.
Explaining the assembly process of the electrodes with reference to FIG. 4, crystalline glass rods 22 of a relatively low melting point are inserted into both sides of amorphous glass rods 21 of a relatively high melting point between the electrodes, and then the sintering process is carried out. Consequently, the crystalline glass rods 22 are melted to wrap the amorphous glass rods 21, thereby acting as an adhesive.
At this time, a gap between both electrodes is maintained as much as a diameter of the amorphous glass rod 21.
However, there is a problem that the electrons can be emitted only when the filament cathode is heated up to a temperature of 750° C. or higher in order for a driving operation. Due to this driving mechanism, 70% or more of the electron beam emitted from the filament cathode in the driving operation is collided against the control electrode and therefore the control electrode is heated to a temperature of 80-150° C. or higher. As a result, there may occur a thermal deformation and a path of the electron beam may be harmfully affected.
To prevent the above problems, an Invar, an expensive metal material of a low thermal expansion, may be used. However, the cost of material is expensive and therefore a manufacturing cost may be increased.
Further, although Korean Patent No. 1999-0048625 discloses a technique of employing a ceramic, there is also a problem that a manufacturing process is very complicated due to a high sintering temperature and the cost of material is very expensive.